(a) Field of the Invention
The present invention relates to a method and apparatus for removing acoustic echo in a teleconference system. More particularly, the present invention relates to a method and apparatus for removing acoustic echo in a teleconference system using a handsfree terminal.
(b) Description of the Related Art
As the demand for convenience in a wireless mobile communication environment increases, interest in handsfree communication and audiovisual communication is also increasing. In such handsfree communication, because of a small and narrow space such as in a vehicle, and in audiovisual communication, because of a short distance between a microphone and a speaker due to down-sizing of a terminal, acoustic echo may occur.
Acoustic echo indicates that a sound signal of another party (far-end talker) that is output from a speaker is changed to an acoustic echo signal through an echo path, is input to a microphone of a user (near-end talker), and is transferred to another party.
In a telepresence system or a teleconference system for smart work, because a conference is implemented using a speaker, it is very important to remove acoustic echo. That is, in a teleconference system, a near-end talker voice signal is bidirectionally transferred, and for example, when implementing a teleconference using a handsfree terminal, an acoustic echo component of a user A (far-end talker) is overlapped with a voice signal of another user B (near-end talker) and is input to a microphone, thereby deteriorating sound quality, and thus in order to improve audio dedicated communication QoS, a function of removing the acoustic echo component is necessary.
A typical method of removing acoustic echo is a method of using a digital adaptive filter. An acoustic echo removing apparatus using an adaptive filter removes an influence of an acoustic echo signal through an echo path from an input voice signal of a microphone using an adaptive filter having an adaptive filter coefficient with reference to a speaker output voice signal. However, the acoustic echo removing apparatus using an adaptive filter has a problem that performance is greatly deteriorated, as distortion such as divergence of an adaptive filter coefficient occurs at a double talk segment. A double talk indicates that a near-end talker voice signal and an acoustic echo signal simultaneously exist at an input voice signal of a microphone, and double talk detection in an acoustic echo removing apparatus is a very important factor. Therefore, in order to prevent such double talk, while a near-end talker voice signal exists, the acoustic echo removing apparatus should temporarily stop updating of an adaptive filter coefficient, and for this purpose, a double talk detection apparatus notifying whether a near-end talker voice signal exists is required.
A double talk detection apparatus generally compares magnitudes of a far-end talker voice signal and an acoustic echo signal that is input to a microphone, and determines that a near-end talker voice signal exists if an acoustic echo signal is relatively larger than a far-end talker voice signal. This method can be simply embodied, but has a drawback that accuracy of double talk detection is deteriorated. Further, when the magnitude of a far-end talker voice signal is small, even if double talk occurs, the magnitude of an acoustic echo signal is not sufficiently large and thus it is difficult to find an accurate time point of double talk.
Another method of detecting double talk calculates a correlation between a near-end talker input signal and a far-end talker voice signal or a correlation between a far-end talker voice signal and an output signal of an adaptive filter and compares the correlations, and when the correlation is equal to or less than a threshold value, this segment is determined to be a double talk segment. However, this method has a high calculation amount, is sensitive to time delay, and requires a proposition condition that an adaptive filter should converge to a predetermined level or more. Further, when an adaptive filter does not converge to a predetermined level or more due to noise existing at a periphery of a near-end talker, there is a drawback that accuracy of double talk detection is deteriorated.